Telephone system



' Jan. 21, 1936.

T. DIMOND TELEPHONE SYSTEM Filed July 18, 1954 m DUUDUBEEIUU It INVENTOR 7'. L. D/MOND ATTORNEY Patented Jan. 21, 1936 l v V a 2,028,195

* umren STATES BA ENT OFFI TELEPHONE SYSTEM Thomas L. Dimond, Boonton, N. ,J., assigiior to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application July s, 1934, Serial No. 735,758

9 Claims. (01.179-18) 1 This invention relates to telephone systems Another feature of the invention is a line and particularly .to those systems in which autofinder switch in which a space discharge device matic switches are ,used for establishing conis usedin circuit with the relay that controlsthe nections. stepping action of the switch magnets. This re- The objects of the invention are to eliminate lay closes the energizing circuits of the magnets some of the individual equipment usually prothrough one of its normal contacts, andthe revided for subscribers lines; to enable the autolay itselfoperates over a circuit through the dismaticswitches to select a subscribers line by charged tube when. the brushes of the switch means of a simple and positive test; toprovide reach the desired level or the desired contact 10, amore reliable testfor controlling the stepping in the level. This arrangement overcomes the action of the switch while hunting for a subpossibility of the switch taking a false step.

scribers line; and to otherwise improvesystems Theforegoing andother features of the invenof this character... Y I tion will be described in detail in' the following It hasbeen proposed heretofore to eliminate specification, which should be taken in conjuncl5, theindividual line relays and to replace them by tion with the accompanying drawing. V

a-prelaymechanism common to a group oflines. The drawing represents schematically a tele- To accomplish this, it has, been necessaryto prophone system in which the features of the invenvide some sort of switching mechanism for astion are embodied and which employs automatic sociating the common relays with any one of the switchesof the well-known two-motion step-bylines when it calls. step type. It is to be understood, however, that 2Q,

. It has also been proposed to use a vacuumtube the embodiment of the invention in this parin common to a group of lines, and. to connect ticular system is given by way of illustration only, the control element through individual resistandflthat the invention may beapplied to autoances to the. respective subscribers" lines, thus matic telephone systems employing other, types 29. doing away'with the individual line relays. An of: switches. arrangement ofthiskind is subject to false op- Referring to the drawing, there are shown a eration due to the combined. elfect of several line calling subscribers, station A and the associated leaks, and it does not lend itself readily ,to a line circuit LC, a line finder switch LF a selecpositive and reliable test to enable the: linefinder tor switch S, a connector switch C, and a called 3% to distinguish and seize the particular line in the subscribers station B. group that is calling. The subscribers stations A and, B are pro- According to thepresent invention these diffie vided with the usual subscriber's set whichis culties are overcome by, means of .asystem in equipped with a dial for controlling the estabwhich a space discharge device having a, multilishment of the, desired connections. The selecplicity of control electrodes is, provided in come tor switch Sand the connector switch C are of mon to a group of subscribers lines. The 'conthe .well-known step-by-step or Strowgertype, trol electrodes, are individual respectively to the and reference may. be had to pages 53 to 67 insubscribers lines. and serve to cause the .dis-, elusive oftheiZndedition of Automatic Telecharge of the devicewhen anyone of saidlines phony. by Smith and Campbell fora detailed .v initiates a call. The common discharge. device description ofthe operation of the circuits asso- 40 causesthe starting of a line finder, to hunt for ciated with these switches. Only those portions thecallingsubscribers line. i of the circuits of the selector and connector .Anotherfeature-of the invention. is a testing switchesare shown that are required for a clear arrangementin which the closure of the lineloop andicomplete description of this invention, the 4 5% at the substation places a potential on the test omitted portions of thesecircuits being indicated terminal of the line in the finder switch at the bybroken lines. 'same timethat the potential of the'findividual .The' line .circuit LC and they line finder switch control electrode isaltelred. This calling poten- LEare shown in 'detailsince the features of the ti'al on the terminal of the finder, permits the invention applyispecifically to these circuits. A

star

otherjlines, and, since the severalcontrol elecmultiplicity of control electrodes, such .as .electrodes are electricallyfisolated from each other, trode' '4,.isassociated with each group of line the calling condition on oneline does not manicircuits. Tube 3 is of the type which breaks down fest itself on the Fterminals'; of any'fo'f the" other and becomes conducting .whenfthe potentiaLon imesm the group. 3 T any onefofits control electrodes becomes sum:

switch, to distinguish the calling line from the cold, cathode gaseous discharge tube 3, having a 5.

ciently positive with respect to the cathode potential of the tube. Each individual line circuit of a group, such as line circuit LC, connects to one of the control electrodes of tube 3, and, when a call is originated by a subscriber, a potential change on the control electrode associated with that line circuit causes tube 3 to break down and cause the line finder switch LP to hunt for the calling line. Current flow in the line also places an identifying potential on the test terminal of calling line to enable the line finder to select the terminals associated with this line.

Each line circuit connects to a set of four terminals appearing in the terminal banks of the line finder switch, as indicated by'the individual line circuit LC which connects to terminals 2|, 22, 23 and 24. The line finder switch LF is of the wellknown step-by-step type provided with a bank of one hundred sets of terminals, such as the set composed 'of terminals 2!, 22, 23 and 24. These terminal sets are arranged in ten vertical levels, each level consisting of ten horizontal terminal sets, and are selectable by brushes I5, I6, I1 and I8, which, by means of a common shaft (not shown), are advanced vertically to the proper level and'then horizontally to the terminals of the calling line under control of the vertical operating magnet I I and the rotary operating magnet 20, respectively. Relay I3, which is connected in the anode circuit of a cold cathode type gaseous discharge tube It), controls the operating circuits for magnets II and 20. The line finder is provided with a commutator 1 having ten conducting segments, one segment for each corresponding level of the line finder bank terminals. Associated with commutator I is a brush 8 which is mounted on the common brush shaft (not shown) and which advances simultaneously with brushes it: to H3 inclusive, during vertical stepping. Tube I0, under control of commutator I and brush 8 during vertical stepping, and under control of test terminal 24 of the calling line and test brush I8 of the line finder during rotary stepping, breaks down when the proper level and the calling line terminals are encountered and causes relay l3 to operate and open theoperating circuits for magnets I I and 20 respectively, thereby preventing the line finder brushes from taking a false additional vertical or rotary step. The operations of these circuits will now be fully set forth in detail in the following description of a call from station A to station B,

The cathode of tube 3 is connected to a source of negative potential, and the anode B is connected to a source of positive potential through the winding of relay I2. The potential difference between the anode and cathode of tube 3, while insufficient to cause the tube to'break down, is sufiicient to maintain ionization of the tube once it isbroken down. Condenser 9 is connected in series with resistance I9 across the anode and cathode of the tube and is therefore charged to a potential equivalent to thepotential difference between those points. The control grid 4 of the tube is connected to negativepotential through resistance 2 and the lower winding of cut-off relay I of line circuit LC, this potential being of the same value as that connected to the cathode 5.

When the receiver is removed from theswitchhook at station A to originate a call, a' circuit is completed from ground over the upper back contact of relay I tipconductor 25, loop of sta-' tionAfring conductor 26, to negative potential over. the lower 'back' contact and through the ionizes.

fiow causes a reduction in the negative potential on the control electrode 4 of tube 3 and on test terminal 24 in the line finder terminal banks. Due to this reduction in potential, control electrode 4 becomes suficiently positive with respect to cathode 5 that tube 3 breaks down and becomes conducting. Relay I2 operates in a circuit from positive potential through its winding, over the anode circuit of tube 3, to negative potential on the cathode of the tube. Immediately upon the breakdown of tube 3, condenser 9 starts to discharge over the anode-cathode circuit of the tube and, when its potential falls below the ionization value of the tube, tube 3 momentarily de- Condenser 9 immediately recharges from the positive potential through the winding of relay I2 and, when its charge reaches the breakdown potential of the tube, tube 3 again ionizes and completes the operating circuit for relay I2 and the discharge circuit for condenser 9. This oscillatory action-continues as long as the potential on the 'control grid 4 remains positive with respect to the potential on cathode 5; Relay I2 is of the slow-to-release type and remains operated even thoughthe current through its winding is pulsating due to the aforementioned actionof tube 3 and condenser 9.

Assume that terminals 2|, 22, 23 and 24, associated with the line circuit of calling station A, are the fifth set of terminals in the fourth level of the line finder switch terminal banks. Tube-3 is common to all of the ten lines appearing in the fourth level of the terminal banks, each of these lines connecting to one of the ten control electrodes of the tube. Relay I2 is therefore commonto all ten lines in the fourth terminal level and functions as a group start relay for .all lines in that level. Relay I2, operating upon the aforementioned breakdown of tube 3 in response to the initiation of the call at station A, connects ground over its left front contact to the fourth conducting segment of commutator I which corresponds to the fourth level of the line switch terminal banks, and connects ground over its right front contact and over the back contact of relay 2'! to battery through the winding of relay I l, operating that relay. 7

Relay I 4, in operating, connects negative potential over its right inner front contact to electrode 3| of gaseous discharge tube It], and op; erates vertical operating magnet II in a circuit from ground over the left back contact of relay 39, right middle front contact of relay I4, back contact of relay l3,right outer back contact of relay 29, to battery through the winding of magnet I I. Vertical magnet I I, in operating, operates relay I3 in a circuit from positive potential through the winding of relay I3 to negative potential over the armature and front contact springs of magnet I I, and, in addition, causes the line finder brushes 8, I5, I6, IT and I8 to make one vertical step. The lower control electrode 32 of tube II] is connected, in a circuit through resistance 33 and over the left outer back contact of relay 29, to the commutator brush 8. On the first vertical step of the brushes, brush 8 contacts the first conducting segment of commutator 1 but, since this segment is open, tube I0 does not func tion at this time. Relay I3, in operating, opens the operating circuit for magnet I I which releases, in turn releasing relay IS. The release of relay I3 again closes the operating circuit for magnet I I which causes the line finder brushes to make the second vertical step. The operation of aoasgras:

magnet: II also operatesrelay I3jwhich'v opens the circuit for magnet II. Magnet II releases, in, turnlreleasing relay I3 which again operates. magnetJI I :and the line finder brushesgmake the third verticalistep. -Magnet II,in operating, operates:

relay I3 whichopens the circuit, through magnet II. Magnet II releases and releases relay I3 of tube I 0. Since negative potential is connected to'the upper cathode 3I over the right inner front contact of relay I4, tube I0 breaks down dueto 201: the potential difference between cathodes 3| and 32. Upon the operation of magnet for the fourth vertical step of the line finder brushes as has just, been set forth, relay I3 operates and opens the .circuit through magnet II. Magnet II 51 releases and completes the circuit from positive potential through the winding of relay I3, over th'e backcontactsofmagnets II and 20, through the right: winding and over the left innerback contact of: relay 29 to anode 35 of tube I0; Since tube IIl'is broken down, as previously stated, relay 29"-operates and relay I3 holds or, if already released, immediately reoperates, in the circuit just traced to the anode 35, to the previously traced negative potential on cathode 3|. Relay I3, operated, holds the energizing circuit for vertical magnet I I open, thereby preventing the line finder brushes from making a false additional vertical step;

The left inner armature and front contact springsof relay 29 are arranged to closebefore any of the back contacts open and relay 29, upon operating through its right winding, looks from battery through its left winding and over its left innerfront contact, to ground over the right outer front contact of relay I4. Relay29, in operating, opens the-operating circuitfor vertical magnet I I and, over its right front contact, partially closes the operating circuit for rotary magnet 20. Relay 29, in operating, also transfers the circuit-of anode 35 of tube I0 from positive potential over the previously traced circuit through the ri'ght winding of relay 29, to the same positive potential in a circuit traceable over the leftmiddle front contact of relay 29, right inner back contact and right winding of relay 30, back contacts of magnets 20 and I I, and through the winding of relay I3.- During the transfer time of the left middle armature of relay 23-from its back toits front contact, the anode circuit of tube Illis -momentarily opened,- thereby causing the tube 7 middlefront contact of relay I4, to ground over the left backcontact of relay 30. Magnet 20, in

energizingcauses brushes I5to I8 inclusive tomake one rotary stepand: contact the first set of--"termi-nals-in-thejfourth level of theJinefinder 7 5i terminal bankse Since it-has beerr assumed thatterminals 2I to 24'inclusive are the fifthVsetaof-F terminals of the fourth level, the testtermina'lsofl': the firstfour'terminal sets are at the. same'poetential as cathode'3l of tube I0. Astest brush. IBJ: encounters these test terminals, tube I0; does not: 5:, function since both cathodes are ,at'equal poten'e tial. Magnet 20, as it operates for each rotary, step of the line finder brushes, operates relay JI3;

in a circuit frominegative potential over itsfronti contact, over the back contact ofmagnet H; to: 101' positive potential through the winding of relayf I3. Relay I3, in operating, opens the operating: circuit for magnet 20 which releases anduconnects the positive potential, throughthe winding,

of relay Bend the right winding of relay 30 over: 15f a previously traced circuit, to the anode 35 0f tube I0. Since tube I0 doesnot break down'i when test brush I8 contacts the test terminals:

of theidle lines, relay I3 immediately: releases: upon each release of magnet 20 as the line finder: 203 brushes rotate across the first four sets of termi-- nals in the fourth level of the terminal banks. Each release of relay I3 again closes the operat-- ing circuit for magnet 20 which energizes and ad vances the brushes to the succeeding setof termlnals. Upon the fifth operation of magnet 20; brushes I5, I6, I! and I8 contact terminals 2|,

22, 23 and respectively of the line circuit=as sociated with the calling station A. As herein before set forth, the potential on test terminal 0 24 islower than the potential on the test terminal of idle' lines due to the voltage drop caused'by the flow of current in the lower winding of relay I. As test brush I8 contacts terminal 24 this'reduced voltage is impressed on control cathode 32.; 35; of tube II] in the circuit over the left outer front: contact of relay 29 and through resistance 33; Since cathode 3| is at full negative potential, the potential difference between cathodes 3Iand 32; causes tube III-to break down and becomecOn -AOI ducting. V

The operation of magnet 20 for thefifth step of the line finder brushes operatesrelay I3 which, in turn, opens the circuit through the winding of the magnet. Magnet 20, in releasing,- closes the previously traced circuit from the posi-'- tive potential through the winding of relay- I3 and through the right winding of relay 30 toanode 35 of tube I0. Sincetube Illis in the con-- ducting condition, relay 30 operates andrelay I 3 remains operated or, if already released, immediately reoperates, in the aforementioned-circuit, over the anode-cathode circuit of tube ID, to -neg--- ative potential on cathode 3I. Relay I3; oper ated, holds the energizing circuit for magnet 20 open and-thereby prevents the line finder brushes from taking a false additional rotary step.-

The left inner armature and front contact springs of relay 30 are so arranged that theyclose before any of the back contacts open, and'relay: 3B, in operating, immediately locksin a circuitfrom battery through its left winding. and over its left inner front contact to ground over the-left front contact of relay I 4. Relay 3ll,'in operating; opens the circuit to the anode 35- of tube I0 thereby de-ionizing the tube andreleaslng relay I3. Relay 30 also opens the operating-ground for magnets I I and 20 over its left backcontact, and closes the tip and ring conductors 36 and:3T from: the line finder bank terminals 2I and 22 over its left and right outer front'contacts respectively,- to the succeeding selector circuit Si Relay 2T operates in a circuit from battery-through its 'left winding, over the right innerfront contac-tsiof't relay-305 to ground overthe lower: armature rs'a-ndli 755:

front contact of the verticalIoff-normalsprings 38'which previously operated upon the first vertical step of the line finder brushes. Relay 2'! opens the circuit to the winding of relay l4 and may under certain conditions lock through its right winding to ground over the start wire 45.

Cut-off relay 1 of line circuit LC also operates,

upon the operation of relay 33, in a circuit from battery through its upper winding, over terminal 23 and brush 1?, right middle front contact of relay30, to ground over the left front contact of relay l4.

Relay 1, in operating, opens the circuit through its lower winding and, since the flow of current through that winding ceases, the potential on control electrode d of tube 3 assumes the full negative value and becomes equal to the potential on cathode 5. As previously set forth, condenser 9 has'been charging and discharging over the anode-cathode circuit of tube 3 in an oscillatory action which has held relay l2 operated in the tube anode circuit. With no difference in the potentials on control cathode 5 and cathode 5, tube 3 de-ionizes and becomes non-conducting as its anode potential falls below the ionization value during the next discharge of condenser 9. With tube 3 in the non-conducting condition, relay l2 releases and removes the ground from segment 36 of commutator l and also opens the circuit through the right winding of relay 2?.

When the tip and ring conductors 36 and 3! respectively, are extended to the selector switch S by the operation of relay 3%, the selector S functions and returns a ground over lead'28 forthe purpose of holding relays l and 3t operated. As previously stated, the operation of relay 2! opens the circuit through the winding of relay H5. Relay l4, being slow to release, maintains the holding ground for the left winding of relay '39 and for the upper winding of relay I until selector S functions and returns ground for this purpose over conductor 28. Relay I4 releases after an interval, and opens the circuit through the left winding of relay 29. Relay 29 releases and partially closes the future operating circuit for release magnet 39.

Under control of dial impulses from the calling station A, the selector switch S and connector switch C function and complete the connection to the called station B.

At the conclusion of the conversation, when the subscribers replace their receivers ground is removed from conductor 28 by the selector circuit S, thereby releasing relays i and 30. Relay 3!], in releasing, opens the tip and ring conductors 35 and 31, and energizes the release magnet 39 in a circuit from battery through the winding of that,

magnet, upper armature and front contact of springs 38, right inner back contact of relay 29, right outer back contact of relay 30, left back contact of relay M to ground over the lower make contact of springs 38. Release magnet 39, in energizing, causes line finder brushes 8, i5, i6, H and [8 to restore to their normal position. As the brushes return to normal, the verticaloff-normal springs 38 restore to normal thereby releasing magnet 39 and relay 2?. Relay 21, in releasing, againcloses the circuit from the winding of relay M 'to the right front contact of the group start relay l2, and the line finder is ready to hunt for another calling line. nects ground over its upper back contact to the tip line conductor 25, and connects negative potential through its lower winding and over its lower back contact to ring line conductor 26- Relay I, in releasing, conthereby restoring line circuit LC to its normal idle condition.

It will be noted that the circuit from the winding of relay l3 .to the anode 35 of the tube I is carried over the back contacts of vertical magnet ll and rotary magnet 20. During the Vertical and horizontal stepping of the brushes, theanode circuit of tube 10 is therefore held open for an interval until the release of magnet II or 20, as the case may be, closes its back contact. This interval is provided to prevent relay l3 from operating too soon due to the overthrow of the brushes during stepping, at which time the brushes may momentarily contact the succeeding segment or set of line terminals before coming to rest in the proper position associated with the particular step taken. For example, during the third vertical step of the brushes, brush 1 may momentarily overthrow to segment 34 before coming to rest on the third segment. Tube I0 may break down momentarily but, since its anode circuit is open at the back contact of vertical magnet H which is not yet released, relay I3 can not operate and stop the vertical stepping prematurely. Similarly, during rotary stepping, the overthrow of brush is to test terminal 24 during the preceding rotary step may momentarily cause tube I!) to break down but in this case the operated rotary magnet 25 holds open the anode circuit and relay l3 can not operate to cause a premature stopping of rotary hunting. In either case, by the time that magnet H or magnet 20 releases and closes the anode circuit for tube Ill, brush l or 8 will have come to rest on the proper segment or terminal.

Resistance I9 is provided in the discharge circuit for condenser 9 to limit the anode current through tube 3. Resistance 33 is provided to limit the current flow between the cathodes of tube It. Resistance it serves to stabilize the potential of control electrode 32.

As hereinbefore set forth, condenser 9 provides for the oscillatory action of tube 3 which insures the release of relay !2 after the control cathode 4. of the tube assumes the same potential as cathode 5. The positive potential connected to cathode may be supplied over the contacts of a high speed interrupter (not shown) in which case condenser 9 and resistance ii) are omitted. Relay l2, being slow-to-release, holds over the interruptions upon the breakdown of tube 3 and, after the control cathode potential returns to the same value as the potential on cathode 5, tube 3 de-ionizes and becomes nonconducting during the first open period of the interrupted positive potential on cathode 5. Tube 3, de-ionized, opens its anode circuit and releases relay l2.

What is claimed is:

1. The combination in a telephone system of lines, a discharge device common to a plurality of said lines and having a plurality of control electrodes, said electrodes being individual respectively to said lines, and switching means responsive to said discharge device.

2. In combination in a telephone system of subscribers lines, a space discharge device common to a group of said lines, said device having a plurality of control electrodes individual respectively to said lines, means for altering the electrical condition of any one of said electrodes under the control of the corresponding line, a discharge circuit for said device, and current responsive means in said discharge circuit.

3. The combination in a telephone system of subscribers lines, a space discharge device common to a group of said lines, a discharge circuit for said device, said device having a plurality of control electrodes individual respectively to said lines, means for maintaining a potential on each of said electrodes to prevent the flow of current in said discharge circuit, means for altering the potential of any one of said electrodes under the control of the corresponding line, and means in said circuit responsive to the flow of current therein.

4, In a telephone system, subscribers lines, a space discharge tube common to a group of said lines, said tube having a plurality of control electrodes individual respectively to said lines, a line finder switch having a terminal bank in which the lines of said. group appear, a circuit controlled by one of said lines when calling for altering the potential of the corresponding control electrode to cause the discharge of said tube and for alter ing the potential of the corresponding terminal in said finder switch, and means responsive to the discharge of said tube for setting said finder switch in operation to seize the terminals of the calling line.

5. In a telephone system, a group of lines, a space discharge tube having a plurality of control electrodes individual respectively to said lines; a space circuit for said tube, a line finder switch having a terminal bank in which said lines appear, means for maintaining a given potential on each of said control electrodes and on each of the terminals of said lines in said finder switch, means controlled over the conductors of a calling one of said lines for altering the potential on the corresponding control electrode to cause the discharge of said tube and for altering the potential on the corresponding terminal of said line in the finder switch, a relay in said space circuit responsive to the discharge of said tube, means controlled by said relay for starting said finder switch in operation, and test means rendered efiective when the finder switch reaches the terminals of the calling line for stopping the movement of said switch.

6. The combination in a selective switch of a terminal bank and a set of brushes including a test brush, a magnet for stepping said brushes over said terminals, 'a stepping relay, an energizing circuit for said magnet extending through a normal contact of said relay, a space discharge device connected to said test brush, and a circuit through said discharge device for operating said relay.

7. The combination in a selective switch of a series of terminals and a set of brushes including a test brush, a magnet for stepping said brushes over said terminals, a stepping relay for controlling the stepping action of said magnet, an energizing circuit for said magnet, extending through a normal contact of said relay, an energizing circuit for said relay extending through a normal contact of said magnet, a space discharge tube in the circuit of said relay, and means for causing said tube to discharge when the brushes of said switch reach a desired set of terminals.

8. The combination with a plurality of lines of a discharge device having a plurality of control electrodes, said electrodes being individual respectively .to said lines, means for altering the potential of one of said electrodes, means effective in response to the altered potential of one of said electrodes for causing said device to discharge repeatedly, and operating means responsive to the discharge of said device.

9. The combination with a plurality of lines of a gas-filled tube having a plurality of control elements, said elements relating respectively to said lines, means for altering the electrical condition of one of said elements, means effective in response to the altered condition of one of said elements for causing said tube to repeatedly and alternately discharge and quench, and means operative in response to the discharge of said tube.

' THOMAS L. DIMOND. 

